The present, competing continuation application aims to continue to develop and test biomarkers of aging in animals obtained from the NIA/NCTR colony. In investigations funded by this grant we have examined age associated alterations in the effect of protein kinase C (PKC) activation on serotonin release in brain slices. We have also examined activity of and translocation of PKC, PKC mediated phosphorylation of membrane proteins, and of the specific membrane PKC substrate, GAP-43. In addition, a number of neurotransmitter-stimulated signal transduction systems have been studied during aging. These include, membrane G protein activation, phosphoinositide hydrolysis and PKC translocation. In these investigations we have observed that diet restriction prevents or retards age-associated changes in some but not all the studied parameters. The investigations to date strongly suggest and lead us to hypothesize that coupling of neurotransmitter receptors to various membrane transduction systems is compromised progressively during aging and that life long diet restriction can prevent, delay or not influence these processes. The proposed investigations specifically aim to (1) further define age related markers associated with neurotransmitter-activated signal transduction systems,. (2) continue to test the effect of diet restriction on these biomarkers, (3) extend the development of blood platelet and lymphocyte as models in studies of transmembrane signal transduction systems-PKC translocation, G protein activation, and phosphoinositide hydrolysis. Experiments are also proposed to explore the molecular mechanisms which underlie these age and diet related changes. In addition, the generalizability of the above systems as biomarkers in aging organisms will be tested in both male and female rats of the following genotypes: F344, B-N and FXB-N hybrids. The proposed investigations will enhance our understanding of the fundamental role of signal transduction in regulating cellular physiology during aging and its applicability in assessing potential interventions of aging processes. The studies will also examine the suitability of these markers for human investigations in easily accessible blood cells.